logo.gif (3296 bytes)Introduction to Protein Structure

Resonance of the Peptide Unit

The amide structure has two resonance contributors:  

wpeF.jpg (2294 bytes)

Because the bond between the carbonyl carbon and the nitrogen has a partial double bond character, rotation around this bond  is restricted.  Thus, the peptide unit is a planar, rigid structure and rotation in the peptide backbone is restricted to the bonds involving the a carbon:

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The rigid, planar nature of the peptide unit has implications for the detailed three-dimensional strcutrue of peptides, as we will see later.

Copyright 1998, 1999, 2007 by Frank R. Gorga;   Page maintained by F.R. Gorga;   Last updated: 12-Mar-2007